The present invention relates generally to a linear drive for a transportation system and, especially, involves a linear drive for an elevator installation.
The elevator car, the counterbalance weight and the doors in an elevator system typically are driven by rotary electric motors. The elevator car and the counterbalance weight are attached to opposite ends of a cable extending over a pulley or sheave driven in rotation by a rotary motor. The elevator doors are attached to belts extending around friction disks driven in rotation by a rotary motor. Linear drives are also used for driving elevator doors. With linear drives or with friction drives, the motor is driving the cable that connects the elevator car and the counterbalance over a return pulley. With the friction wheel drive principle or the linear magnet principle, the cable is connected at the elevator car. All drive types also require independent safety devices in case the drive fails and the elevator car begins to drop. The safety device must brake the elevator car from a certain overspeed and smoothly bring the car to a stop.
A disadvantage of the known equipment is that a complex mechanical system is necessary for the drive and for the safety device with many individual parts. As a consequence of the mechanical complexity, such equipment is expensive to manufacture and maintain, as well as is more likely to break down disturbing the service.